This invention relates to the construction of pocketed spring mattress cores and more particularly to a method of assembling pocketed coil springs into a mattress core.
It is known to place strings of pocketed coil springs in a parallel fashion to create a mattress, inner spring unit or other body support foundation. A number of coils in a string or row and the number of rows are dependent upon the coil spring diameter and the desired finished size of the mattress or the like. The construction may be a plurality of rows of parallel coils with the coils aligned in columns so that the coils line up in both longitudinal and lateral directions, or they may be nested in a honeycomb configuration wherein coils in one row are off-set from coils in the adjacent row. Moreover, the strings of coils may be separated by strips of various types of material such as polyurethane foam or other flexible materials as illustrated in Breckle et al U.S. Pat. No. 4,907,309 and German Patent No. DE 4031652. The strings of coils are commonly connected by adhesives on the sides of the coils as illustrated in Stumpf U.S. Pat. Nos. 4,566,926 and 4,578,834, and Suenens et al. U.S. Pat. Nos. 5,016,305 and 5,637,178. A nestled construction where strings of coils are interlocked are illustrated in Stumpf U.S. Pat. No. 5,319,815 and German 4,040,220. Other methods of connecting the strings of coils utilize metal clips known as hog rings or they may be stitched with twine which penetrates each string of coils.
A non-patented method in the prior art is the use of strings of coils connected by a web of nonwoven material secured by adhesive to the top and bottom of the pocketed coil units, the adhesive being applied by manually controlled or automatically controlled spray nozzles. Alternatively, or in addition, to the spraying method, beads of hot melt adhesive may be dispensed onto the top and bottom surfaces of the strings of coils or onto top and bottom sheets of nonwoven material and the sheets of nonwoven material then pressed against the adhesive top and bottom surfaces of the strings of coils.
In the prior art processes, control and distribution of the adhesive is difficult and inefficient. Some areas of the coil strings may receive too much adhesive while other areas may not receive a sufficient amount of adhesive. Excess adhesive of course is economically inefficient, while risk of separation of the pocketed coil strings from the nonwoven material may result from too little adhesive. Moreover, when adhesive is sprayed there is a tendency for the spray nozzles to clog so that the flow of glue is obstructed. This results in a time consuming cleaning and maintenance program. Additionally, hot melt spraying requires the system to be heated about one hour before spraying can begin. Other difficulties presented by hot melt spraying and application of beads is that the hoses through which the hot melt flows must be insulated to maintain the temperature of the glue within the hose, thereby resulting in very heavy hoses. Since the spraying process involves manually moving the spray nozzle to which the hose is attached to spray the adhesive, the heavy hoses result in the process being slow and fatiguing to the operators who often encounter minor burns from the glue and the nozzles.